1. Field of the Invention
The present invention relates to a process for producing an .alpha.-hydroxycarboxylic acid amide. More specifically, it relates to a process for producing an .alpha.-hydroxycarboxylic acid amide by a hydration reaction of cyanohydrin in liquid phase.
.alpha.-Hydroxycarboxylic acid amide becomes a starting material for the production of .alpha., .beta.-unsaturated carboxylate via .alpha.-hydroxycarboxylate. In particular, when .alpha.-hydroxysobutyramide is used as a starting material, methyl methacrylate can be obtained via methyl .alpha.-hydroxyisobutyrate which is finally converted into poly(methyl methacrylate), having an excellent resin characteristic and industrially great importance and uses.
2. Description of the Related Arts
As a catalyst for a hydration reaction of cyanohydrin to produce the corresponding .alpha.-hydroxycarboxylic acid amide, manganese dioxide is disclosed in West Germany Pat. No. 2,131,813. In addition, .delta.-type manganese dioxide used as a catalyst for a hydration reaction of acetone cyanohydrin is disclosed in U.S. Pat. No. 4,018,829.
Moreover, Japanese patent application Laid-Open Nos. 57534/1988 and 57535/1988 disclosed methods for preparing manganese dioxide catalysts in which zinc is incorporated into manganese dioxide or potassium permanganate is reduced with hydrochloric acid. However, when the manganese dioxide prepared by the above methods is used as a catalyst as it was in the reaction, there are problems in that catalytic activity is insufficient so a large amount of the catalyst is required to be used, the yield of the desired amide is low, and the catalytic activity is rapidly lowered in a relatively short period of time. Accordingly, the above manganese dioxide has not yet been used in practice.
The present inventors have found that an activity and a lifetime of a manganese dioxide catalyst are closely related to the amounts of an alkali metal element and/or an alkaline earth element caused to coexist in the catalyst when producing .alpha.-hydroxycarboxylic acid amide from cyanohydrin. In addition, present inventors have found that the lifetime of the catalyst can be improved by adjusting the hydrogen ion concentration (pH) of a starting material for the hydration reaction. The present invention can be accomplished based on the above findings.